1. Field of the Invention
The invention relates to an in-vivo image capturing system such as a capsule endoscope which is inserted into a body of a subject in order to obtain images of inside the subject.
2. Description of the Related Art
In recent years, swallowable capsule endoscopes are developed in the field of endoscopes. Provided with an imaging function and a radio function, the capsule endoscope passes through the internal organs such as esophagus, stomach, and a small intestine with peristaltic motion and obtains images sequentially from the time when a patient swallows it from the mouth for observation of the body cavity until it is naturally discharged from the body.
For example, according to Japanese Patent Application Laid-Open No. 2003-19111, while the capsule endoscope is moving inside the body cavity, image data obtained within the body by the capsule endoscope is sequentially transmitted to the outside of the body through radio communication and stored in a memory set in a receiving device outside the body. A doctor or a registered nurse may make a diagnosis based on the images displayed on a display according to the image data stored in the memory.
In this kind of capsule endoscope, a monocular capsule endoscope is generally used, in which an imaging device such as a CCD is mounted only on one side and it may obtain images only in one direction (one end direction). The monocular capsule endoscope, however, is difficult to determine an imaging direction thereof because the capsule endoscope swallowed doesn't proceed in a constant direction within the body. For example, assume that a user wants to obtain images of a cardiac portion of the stomach passing behind the esophagus to observe this portion downwardly after a patient swallows the capsule endoscope. In this case, when the capsule endoscope proceeds inside the body with the imaging direction headed reversely (upward or in a trailing direction), the capsule endoscope may not meet this desire.
In these days, a pantoscopic (or binocular) capsule endoscope which may obtain images in the both backward and forward direction (at the both ends) is also proposed in United States Patent Application Publication No. 2004/199061. According to the pantoscopic capsule endoscope, since the images in the backward and forward direction may be obtained in the forwarding direction, it does not matter that the capsule endoscope proceeds in any direction.
In the case of the pantoscopic capsule endoscope, however, a user has to observe a large amount of images obtained backward and forward on a display and the like later. Generally, even in the case of the monocular capsule endoscope, it takes a long time to observe images, and in the case of the pantoscopic endoscope, it takes an extravagant time. In the case of the pantoscopic capsule endoscope, the obtained image data is twice as much as that in the case of the monocular capsule endoscope through simple calculation, and it is necessary to transmit the data from the capsule endoscope to the receiver in a band wider than that of the monocular capsule endoscope, which increases restriction.